/*
   *  Kernel Probes (KProbes)
   *  kernel/kprobes.c
   *
   * This program is free software; you can redistribute it and/or modify
   * it under the terms of the GNU General Public License as published by
   * the Free Software Foundation; either version 2 of the License, or
   * (at your option) any later version.
   *
   * This program is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU General Public License for more details.
   *
   * You should have received a copy of the GNU General Public License
   * along with this program; if not, write to the Free Software
   * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
   *
   * Copyright (C) IBM Corporation, 2002, 2004
   *
   * 2002-Oct	Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
   *		Probes initial implementation (includes suggestions from
   *		Rusty Russell).
   * 2004-Aug	Updated by Prasanna S Panchamukhi <prasanna@in.ibm.com> with
   *		hlists and exceptions notifier as suggested by Andi Kleen.
   * 2004-July	Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
   *		interface to access function arguments.
   * 2004-Sep	Prasanna S Panchamukhi <prasanna@in.ibm.com> Changed Kprobes
   *		exceptions notifier to be first on the priority list.

   * 2005-May	Hien Nguyen <hien@us.ibm.com>, Jim Keniston
   *		<jkenisto@us.ibm.com> and Prasanna S Panchamukhi
   *		<prasanna@in.ibm.com> added function-return probes.

   */
  #include <linux/kprobes.h>

  #include <linux/hash.h>
  #include <linux/init.h>

  #include <linux/slab.h>

  #include <linux/stddef.h>

  #include <linux/module.h>

  #include <linux/moduleloader.h>

  #include <linux/kallsyms.h>

  #include <linux/freezer.h>

  #include <linux/seq_file.h>
  #include <linux/debugfs.h>

  #include <linux/sysctl.h>

  #include <linux/kdebug.h>

  #include <linux/memory.h>

  #include <linux/ftrace.h>

  #include <linux/cpu.h>

  #include <linux/jump_label.h>

  #include <asm-generic/sections.h>

  #include <asm/cacheflush.h>
  #include <asm/errno.h>

  #include <asm/uaccess.h>

  
  #define KPROBE_HASH_BITS 6
  #define KPROBE_TABLE_SIZE (1 << KPROBE_HASH_BITS)

  
  /*
   * Some oddball architectures like 64bit powerpc have function descriptors
   * so this must be overridable.
   */
  #ifndef kprobe_lookup_name
  #define kprobe_lookup_name(name, addr) \
  	addr = ((kprobe_opcode_t *)(kallsyms_lookup_name(name)))
  #endif

  static int kprobes_initialized;

  static struct hlist_head kprobe_table[KPROBE_TABLE_SIZE];

  static struct hlist_head kretprobe_inst_table[KPROBE_TABLE_SIZE];

  /* NOTE: change this value only with kprobe_mutex held */

  static bool kprobes_all_disarmed;

  /* This protects kprobe_table and optimizing_list */
  static DEFINE_MUTEX(kprobe_mutex);

  static DEFINE_PER_CPU(struct kprobe *, kprobe_instance) = NULL;

  static struct {

  	spinlock_t lock ____cacheline_aligned_in_smp;

  } kretprobe_table_locks[KPROBE_TABLE_SIZE];
  
  static spinlock_t *kretprobe_table_lock_ptr(unsigned long hash)
  {
  	return &(kretprobe_table_locks[hash].lock);
  }

  /*
   * Normally, functions that we'd want to prohibit kprobes in, are marked
   * __kprobes. But, there are cases where such functions already belong to
   * a different section (__sched for preempt_schedule)
   *
   * For such cases, we now have a blacklist
   */

  static struct kprobe_blackpoint kprobe_blacklist[] = {

  	{"preempt_schedule",},

  	{"native_get_debugreg",},

  	{"irq_entries_start",},
  	{"common_interrupt",},

  	{"mcount",},	/* mcount can be called from everywhere */

  	{NULL}    /* Terminator */
  };

  #ifdef __ARCH_WANT_KPROBES_INSN_SLOT

  /*
   * kprobe->ainsn.insn points to the copy of the instruction to be
   * single-stepped. x86_64, POWER4 and above have no-exec support and
   * stepping on the instruction on a vmalloced/kmalloced/data page
   * is a recipe for disaster
   */

  struct kprobe_insn_page {

  	struct list_head list;

  	kprobe_opcode_t *insns;		/* Page of instruction slots */

  	int nused;

  	int ngarbage;

  	char slot_used[];

  };

  #define KPROBE_INSN_PAGE_SIZE(slots)			\
  	(offsetof(struct kprobe_insn_page, slot_used) +	\
  	 (sizeof(char) * (slots)))
  
  struct kprobe_insn_cache {
  	struct list_head pages;	/* list of kprobe_insn_page */
  	size_t insn_size;	/* size of instruction slot */
  	int nr_garbage;
  };
  
  static int slots_per_page(struct kprobe_insn_cache *c)
  {
  	return PAGE_SIZE/(c->insn_size * sizeof(kprobe_opcode_t));
  }

  enum kprobe_slot_state {
  	SLOT_CLEAN = 0,
  	SLOT_DIRTY = 1,
  	SLOT_USED = 2,
  };

  static DEFINE_MUTEX(kprobe_insn_mutex);	/* Protects kprobe_insn_slots */
  static struct kprobe_insn_cache kprobe_insn_slots = {
  	.pages = LIST_HEAD_INIT(kprobe_insn_slots.pages),
  	.insn_size = MAX_INSN_SIZE,
  	.nr_garbage = 0,
  };
  static int __kprobes collect_garbage_slots(struct kprobe_insn_cache *c);

  /**

   * __get_insn_slot() - Find a slot on an executable page for an instruction.

   * We allocate an executable page if there's no room on existing ones.
   */

  static kprobe_opcode_t __kprobes *__get_insn_slot(struct kprobe_insn_cache *c)

  {
  	struct kprobe_insn_page *kip;

   retry:

  	list_for_each_entry(kip, &c->pages, list) {
  		if (kip->nused < slots_per_page(c)) {

  			int i;

  			for (i = 0; i < slots_per_page(c); i++) {

  				if (kip->slot_used[i] == SLOT_CLEAN) {
  					kip->slot_used[i] = SLOT_USED;

  					kip->nused++;

  					return kip->insns + (i * c->insn_size);

  				}
  			}

  			/* kip->nused is broken. Fix it. */
  			kip->nused = slots_per_page(c);
  			WARN_ON(1);

  		}
  	}

  	/* If there are any garbage slots, collect it and try again. */

  	if (c->nr_garbage && collect_garbage_slots(c) == 0)

  		goto retry;

  
  	/* All out of space.  Need to allocate a new page. */
  	kip = kmalloc(KPROBE_INSN_PAGE_SIZE(slots_per_page(c)), GFP_KERNEL);

  	if (!kip)

  		return NULL;

  
  	/*
  	 * Use module_alloc so this page is within +/- 2GB of where the
  	 * kernel image and loaded module images reside. This is required
  	 * so x86_64 can correctly handle the %rip-relative fixups.
  	 */
  	kip->insns = module_alloc(PAGE_SIZE);
  	if (!kip->insns) {
  		kfree(kip);
  		return NULL;
  	}

  	INIT_LIST_HEAD(&kip->list);

  	memset(kip->slot_used, SLOT_CLEAN, slots_per_page(c));

  	kip->slot_used[0] = SLOT_USED;

  	kip->nused = 1;

  	kip->ngarbage = 0;

  	list_add(&kip->list, &c->pages);

  	return kip->insns;
  }

  kprobe_opcode_t __kprobes *get_insn_slot(void)
  {

  	kprobe_opcode_t *ret = NULL;

  	mutex_lock(&kprobe_insn_mutex);

  	ret = __get_insn_slot(&kprobe_insn_slots);

  	mutex_unlock(&kprobe_insn_mutex);

  	return ret;
  }

  /* Return 1 if all garbages are collected, otherwise 0. */
  static int __kprobes collect_one_slot(struct kprobe_insn_page *kip, int idx)
  {

  	kip->slot_used[idx] = SLOT_CLEAN;

  	kip->nused--;
  	if (kip->nused == 0) {
  		/*
  		 * Page is no longer in use.  Free it unless
  		 * it's the last one.  We keep the last one
  		 * so as not to have to set it up again the
  		 * next time somebody inserts a probe.
  		 */

  		if (!list_is_singular(&kip->list)) {

  			list_del(&kip->list);

  			module_free(NULL, kip->insns);
  			kfree(kip);
  		}
  		return 1;
  	}
  	return 0;
  }

  static int __kprobes collect_garbage_slots(struct kprobe_insn_cache *c)

  {

  	struct kprobe_insn_page *kip, *next;

  	/* Ensure no-one is interrupted on the garbages */
  	synchronize_sched();

  	list_for_each_entry_safe(kip, next, &c->pages, list) {

  		int i;

  		if (kip->ngarbage == 0)
  			continue;
  		kip->ngarbage = 0;	/* we will collect all garbages */

  		for (i = 0; i < slots_per_page(c); i++) {

  			if (kip->slot_used[i] == SLOT_DIRTY &&

  			    collect_one_slot(kip, i))
  				break;
  		}
  	}

  	c->nr_garbage = 0;

  	return 0;
  }

  static void __kprobes __free_insn_slot(struct kprobe_insn_cache *c,
  				       kprobe_opcode_t *slot, int dirty)

  {
  	struct kprobe_insn_page *kip;

  	list_for_each_entry(kip, &c->pages, list) {

  		long idx = ((long)slot - (long)kip->insns) /
  				(c->insn_size * sizeof(kprobe_opcode_t));

  		if (idx >= 0 && idx < slots_per_page(c)) {
  			WARN_ON(kip->slot_used[idx] != SLOT_USED);

  			if (dirty) {

  				kip->slot_used[idx] = SLOT_DIRTY;

  				kip->ngarbage++;

  				if (++c->nr_garbage > slots_per_page(c))
  					collect_garbage_slots(c);

  			} else

  				collect_one_slot(kip, idx);
  			return;

  		}
  	}

  	/* Could not free this slot. */
  	WARN_ON(1);
  }

  void __kprobes free_insn_slot(kprobe_opcode_t * slot, int dirty)
  {
  	mutex_lock(&kprobe_insn_mutex);
  	__free_insn_slot(&kprobe_insn_slots, slot, dirty);

  	mutex_unlock(&kprobe_insn_mutex);

  }

  #ifdef CONFIG_OPTPROBES
  /* For optimized_kprobe buffer */
  static DEFINE_MUTEX(kprobe_optinsn_mutex); /* Protects kprobe_optinsn_slots */
  static struct kprobe_insn_cache kprobe_optinsn_slots = {
  	.pages = LIST_HEAD_INIT(kprobe_optinsn_slots.pages),
  	/* .insn_size is initialized later */
  	.nr_garbage = 0,
  };
  /* Get a slot for optimized_kprobe buffer */
  kprobe_opcode_t __kprobes *get_optinsn_slot(void)
  {
  	kprobe_opcode_t *ret = NULL;
  
  	mutex_lock(&kprobe_optinsn_mutex);
  	ret = __get_insn_slot(&kprobe_optinsn_slots);
  	mutex_unlock(&kprobe_optinsn_mutex);
  
  	return ret;
  }
  
  void __kprobes free_optinsn_slot(kprobe_opcode_t * slot, int dirty)
  {
  	mutex_lock(&kprobe_optinsn_mutex);
  	__free_insn_slot(&kprobe_optinsn_slots, slot, dirty);
  	mutex_unlock(&kprobe_optinsn_mutex);
  }
  #endif

  #endif

  /* We have preemption disabled.. so it is safe to use __ versions */
  static inline void set_kprobe_instance(struct kprobe *kp)
  {

  	__this_cpu_write(kprobe_instance, kp);

  }
  
  static inline void reset_kprobe_instance(void)
  {

  	__this_cpu_write(kprobe_instance, NULL);

  }

  /*
   * This routine is called either:

   * 	- under the kprobe_mutex - during kprobe_[un]register()

   * 				OR

   * 	- with preemption disabled - from arch/xxx/kernel/kprobes.c

   */

  struct kprobe __kprobes *get_kprobe(void *addr)

  {
  	struct hlist_head *head;
  	struct hlist_node *node;

  	struct kprobe *p;

  
  	head = &kprobe_table[hash_ptr(addr, KPROBE_HASH_BITS)];

  	hlist_for_each_entry_rcu(p, node, head, hlist) {

  		if (p->addr == addr)
  			return p;
  	}

  	return NULL;
  }

  static int __kprobes aggr_pre_handler(struct kprobe *p, struct pt_regs *regs);
  
  /* Return true if the kprobe is an aggregator */
  static inline int kprobe_aggrprobe(struct kprobe *p)
  {
  	return p->pre_handler == aggr_pre_handler;
  }

  /* Return true(!0) if the kprobe is unused */
  static inline int kprobe_unused(struct kprobe *p)
  {
  	return kprobe_aggrprobe(p) && kprobe_disabled(p) &&
  	       list_empty(&p->list);
  }

  /*
   * Keep all fields in the kprobe consistent
   */

  static inline void copy_kprobe(struct kprobe *ap, struct kprobe *p)

  {

  	memcpy(&p->opcode, &ap->opcode, sizeof(kprobe_opcode_t));
  	memcpy(&p->ainsn, &ap->ainsn, sizeof(struct arch_specific_insn));

  }
  
  #ifdef CONFIG_OPTPROBES

  /* NOTE: change this value only with kprobe_mutex held */
  static bool kprobes_allow_optimization;

  /*
   * Call all pre_handler on the list, but ignores its return value.
   * This must be called from arch-dep optimized caller.
   */
  void __kprobes opt_pre_handler(struct kprobe *p, struct pt_regs *regs)
  {
  	struct kprobe *kp;
  
  	list_for_each_entry_rcu(kp, &p->list, list) {
  		if (kp->pre_handler && likely(!kprobe_disabled(kp))) {
  			set_kprobe_instance(kp);
  			kp->pre_handler(kp, regs);
  		}
  		reset_kprobe_instance();
  	}
  }

  /* Free optimized instructions and optimized_kprobe */
  static __kprobes void free_aggr_kprobe(struct kprobe *p)
  {
  	struct optimized_kprobe *op;
  
  	op = container_of(p, struct optimized_kprobe, kp);
  	arch_remove_optimized_kprobe(op);
  	arch_remove_kprobe(p);
  	kfree(op);
  }

  /* Return true(!0) if the kprobe is ready for optimization. */
  static inline int kprobe_optready(struct kprobe *p)
  {
  	struct optimized_kprobe *op;
  
  	if (kprobe_aggrprobe(p)) {
  		op = container_of(p, struct optimized_kprobe, kp);
  		return arch_prepared_optinsn(&op->optinsn);
  	}
  
  	return 0;
  }

  /* Return true(!0) if the kprobe is disarmed. Note: p must be on hash list */
  static inline int kprobe_disarmed(struct kprobe *p)
  {
  	struct optimized_kprobe *op;
  
  	/* If kprobe is not aggr/opt probe, just return kprobe is disabled */
  	if (!kprobe_aggrprobe(p))
  		return kprobe_disabled(p);
  
  	op = container_of(p, struct optimized_kprobe, kp);
  
  	return kprobe_disabled(p) && list_empty(&op->list);
  }
  
  /* Return true(!0) if the probe is queued on (un)optimizing lists */
  static int __kprobes kprobe_queued(struct kprobe *p)
  {
  	struct optimized_kprobe *op;
  
  	if (kprobe_aggrprobe(p)) {
  		op = container_of(p, struct optimized_kprobe, kp);
  		if (!list_empty(&op->list))
  			return 1;
  	}
  	return 0;
  }

  /*
   * Return an optimized kprobe whose optimizing code replaces
   * instructions including addr (exclude breakpoint).
   */

  static struct kprobe *__kprobes get_optimized_kprobe(unsigned long addr)

  {
  	int i;
  	struct kprobe *p = NULL;
  	struct optimized_kprobe *op;
  
  	/* Don't check i == 0, since that is a breakpoint case. */
  	for (i = 1; !p && i < MAX_OPTIMIZED_LENGTH; i++)
  		p = get_kprobe((void *)(addr - i));
  
  	if (p && kprobe_optready(p)) {
  		op = container_of(p, struct optimized_kprobe, kp);
  		if (arch_within_optimized_kprobe(op, addr))
  			return p;
  	}
  
  	return NULL;
  }
  
  /* Optimization staging list, protected by kprobe_mutex */
  static LIST_HEAD(optimizing_list);

  static LIST_HEAD(unoptimizing_list);

  
  static void kprobe_optimizer(struct work_struct *work);
  static DECLARE_DELAYED_WORK(optimizing_work, kprobe_optimizer);

  static DECLARE_COMPLETION(optimizer_comp);

  #define OPTIMIZE_DELAY 5

  /*
   * Optimize (replace a breakpoint with a jump) kprobes listed on
   * optimizing_list.
   */
  static __kprobes void do_optimize_kprobes(void)

  {

  	/* Optimization never be done when disarmed */
  	if (kprobes_all_disarmed || !kprobes_allow_optimization ||
  	    list_empty(&optimizing_list))
  		return;

  	/*
  	 * The optimization/unoptimization refers online_cpus via
  	 * stop_machine() and cpu-hotplug modifies online_cpus.
  	 * And same time, text_mutex will be held in cpu-hotplug and here.
  	 * This combination can cause a deadlock (cpu-hotplug try to lock
  	 * text_mutex but stop_machine can not be done because online_cpus
  	 * has been changed)
  	 * To avoid this deadlock, we need to call get_online_cpus()
  	 * for preventing cpu-hotplug outside of text_mutex locking.
  	 */
  	get_online_cpus();
  	mutex_lock(&text_mutex);

  	arch_optimize_kprobes(&optimizing_list);

  	mutex_unlock(&text_mutex);
  	put_online_cpus();

  }

  /*
   * Unoptimize (replace a jump with a breakpoint and remove the breakpoint
   * if need) kprobes listed on unoptimizing_list.
   */
  static __kprobes void do_unoptimize_kprobes(struct list_head *free_list)
  {
  	struct optimized_kprobe *op, *tmp;
  
  	/* Unoptimization must be done anytime */
  	if (list_empty(&unoptimizing_list))
  		return;
  
  	/* Ditto to do_optimize_kprobes */
  	get_online_cpus();
  	mutex_lock(&text_mutex);

  	arch_unoptimize_kprobes(&unoptimizing_list, free_list);
  	/* Loop free_list for disarming */
  	list_for_each_entry_safe(op, tmp, free_list, list) {

  		/* Disarm probes if marked disabled */
  		if (kprobe_disabled(&op->kp))
  			arch_disarm_kprobe(&op->kp);
  		if (kprobe_unused(&op->kp)) {
  			/*
  			 * Remove unused probes from hash list. After waiting
  			 * for synchronization, these probes are reclaimed.
  			 * (reclaiming is done by do_free_cleaned_kprobes.)
  			 */
  			hlist_del_rcu(&op->kp.hlist);

  		} else
  			list_del_init(&op->list);
  	}
  	mutex_unlock(&text_mutex);
  	put_online_cpus();
  }
  
  /* Reclaim all kprobes on the free_list */
  static __kprobes void do_free_cleaned_kprobes(struct list_head *free_list)
  {
  	struct optimized_kprobe *op, *tmp;
  
  	list_for_each_entry_safe(op, tmp, free_list, list) {
  		BUG_ON(!kprobe_unused(&op->kp));
  		list_del_init(&op->list);
  		free_aggr_kprobe(&op->kp);
  	}
  }
  
  /* Start optimizer after OPTIMIZE_DELAY passed */
  static __kprobes void kick_kprobe_optimizer(void)
  {
  	if (!delayed_work_pending(&optimizing_work))
  		schedule_delayed_work(&optimizing_work, OPTIMIZE_DELAY);
  }

  /* Kprobe jump optimizer */
  static __kprobes void kprobe_optimizer(struct work_struct *work)
  {

  	LIST_HEAD(free_list);

  	/* Lock modules while optimizing kprobes */
  	mutex_lock(&module_mutex);
  	mutex_lock(&kprobe_mutex);

  
  	/*

  	 * Step 1: Unoptimize kprobes and collect cleaned (unused and disarmed)
  	 * kprobes before waiting for quiesence period.
  	 */
  	do_unoptimize_kprobes(&free_list);
  
  	/*
  	 * Step 2: Wait for quiesence period to ensure all running interrupts

  	 * are done. Because optprobe may modify multiple instructions
  	 * there is a chance that Nth instruction is interrupted. In that
  	 * case, running interrupt can return to 2nd-Nth byte of jump
  	 * instruction. This wait is for avoiding it.
  	 */
  	synchronize_sched();

  	/* Step 3: Optimize kprobes after quiesence period */

  	do_optimize_kprobes();

  
  	/* Step 4: Free cleaned kprobes after quiesence period */
  	do_free_cleaned_kprobes(&free_list);

  	mutex_unlock(&kprobe_mutex);
  	mutex_unlock(&module_mutex);

  	/* Step 5: Kick optimizer again if needed */

  	if (!list_empty(&optimizing_list) || !list_empty(&unoptimizing_list))

  		kick_kprobe_optimizer();
  	else
  		/* Wake up all waiters */
  		complete_all(&optimizer_comp);

  }
  
  /* Wait for completing optimization and unoptimization */
  static __kprobes void wait_for_kprobe_optimizer(void)
  {
  	if (delayed_work_pending(&optimizing_work))
  		wait_for_completion(&optimizer_comp);

  }
  
  /* Optimize kprobe if p is ready to be optimized */
  static __kprobes void optimize_kprobe(struct kprobe *p)
  {
  	struct optimized_kprobe *op;
  
  	/* Check if the kprobe is disabled or not ready for optimization. */

  	if (!kprobe_optready(p) || !kprobes_allow_optimization ||

  	    (kprobe_disabled(p) || kprobes_all_disarmed))
  		return;
  
  	/* Both of break_handler and post_handler are not supported. */
  	if (p->break_handler || p->post_handler)
  		return;
  
  	op = container_of(p, struct optimized_kprobe, kp);
  
  	/* Check there is no other kprobes at the optimized instructions */
  	if (arch_check_optimized_kprobe(op) < 0)
  		return;
  
  	/* Check if it is already optimized. */
  	if (op->kp.flags & KPROBE_FLAG_OPTIMIZED)
  		return;

  	op->kp.flags |= KPROBE_FLAG_OPTIMIZED;

  
  	if (!list_empty(&op->list))
  		/* This is under unoptimizing. Just dequeue the probe */
  		list_del_init(&op->list);
  	else {
  		list_add(&op->list, &optimizing_list);
  		kick_kprobe_optimizer();
  	}
  }
  
  /* Short cut to direct unoptimizing */
  static __kprobes void force_unoptimize_kprobe(struct optimized_kprobe *op)
  {
  	get_online_cpus();
  	arch_unoptimize_kprobe(op);
  	put_online_cpus();
  	if (kprobe_disabled(&op->kp))
  		arch_disarm_kprobe(&op->kp);

  }
  
  /* Unoptimize a kprobe if p is optimized */

  static __kprobes void unoptimize_kprobe(struct kprobe *p, bool force)

  {
  	struct optimized_kprobe *op;

  	if (!kprobe_aggrprobe(p) || kprobe_disarmed(p))
  		return; /* This is not an optprobe nor optimized */
  
  	op = container_of(p, struct optimized_kprobe, kp);
  	if (!kprobe_optimized(p)) {
  		/* Unoptimized or unoptimizing case */
  		if (force && !list_empty(&op->list)) {
  			/*
  			 * Only if this is unoptimizing kprobe and forced,
  			 * forcibly unoptimize it. (No need to unoptimize
  			 * unoptimized kprobe again :)
  			 */

  			list_del_init(&op->list);

  			force_unoptimize_kprobe(op);
  		}
  		return;
  	}
  
  	op->kp.flags &= ~KPROBE_FLAG_OPTIMIZED;
  	if (!list_empty(&op->list)) {
  		/* Dequeue from the optimization queue */
  		list_del_init(&op->list);
  		return;
  	}
  	/* Optimized kprobe case */
  	if (force)
  		/* Forcibly update the code: this is a special case */
  		force_unoptimize_kprobe(op);
  	else {
  		list_add(&op->list, &unoptimizing_list);
  		kick_kprobe_optimizer();

  	}
  }

  /* Cancel unoptimizing for reusing */
  static void reuse_unused_kprobe(struct kprobe *ap)
  {
  	struct optimized_kprobe *op;
  
  	BUG_ON(!kprobe_unused(ap));
  	/*
  	 * Unused kprobe MUST be on the way of delayed unoptimizing (means
  	 * there is still a relative jump) and disabled.
  	 */
  	op = container_of(ap, struct optimized_kprobe, kp);
  	if (unlikely(list_empty(&op->list)))
  		printk(KERN_WARNING "Warning: found a stray unused "
  			"aggrprobe@%p
  ", ap->addr);
  	/* Enable the probe again */
  	ap->flags &= ~KPROBE_FLAG_DISABLED;
  	/* Optimize it again (remove from op->list) */
  	BUG_ON(!kprobe_optready(ap));
  	optimize_kprobe(ap);
  }

  /* Remove optimized instructions */
  static void __kprobes kill_optimized_kprobe(struct kprobe *p)
  {
  	struct optimized_kprobe *op;
  
  	op = container_of(p, struct optimized_kprobe, kp);

  	if (!list_empty(&op->list))
  		/* Dequeue from the (un)optimization queue */

  		list_del_init(&op->list);

  
  	op->kp.flags &= ~KPROBE_FLAG_OPTIMIZED;
  	/* Don't touch the code, because it is already freed. */

  	arch_remove_optimized_kprobe(op);
  }
  
  /* Try to prepare optimized instructions */
  static __kprobes void prepare_optimized_kprobe(struct kprobe *p)
  {
  	struct optimized_kprobe *op;
  
  	op = container_of(p, struct optimized_kprobe, kp);
  	arch_prepare_optimized_kprobe(op);
  }

  /* Allocate new optimized_kprobe and try to prepare optimized instructions */
  static __kprobes struct kprobe *alloc_aggr_kprobe(struct kprobe *p)
  {
  	struct optimized_kprobe *op;
  
  	op = kzalloc(sizeof(struct optimized_kprobe), GFP_KERNEL);
  	if (!op)
  		return NULL;
  
  	INIT_LIST_HEAD(&op->list);
  	op->kp.addr = p->addr;
  	arch_prepare_optimized_kprobe(op);
  
  	return &op->kp;
  }
  
  static void __kprobes init_aggr_kprobe(struct kprobe *ap, struct kprobe *p);
  
  /*
   * Prepare an optimized_kprobe and optimize it
   * NOTE: p must be a normal registered kprobe
   */
  static __kprobes void try_to_optimize_kprobe(struct kprobe *p)
  {
  	struct kprobe *ap;
  	struct optimized_kprobe *op;
  
  	ap = alloc_aggr_kprobe(p);
  	if (!ap)
  		return;
  
  	op = container_of(ap, struct optimized_kprobe, kp);
  	if (!arch_prepared_optinsn(&op->optinsn)) {
  		/* If failed to setup optimizing, fallback to kprobe */

  		arch_remove_optimized_kprobe(op);
  		kfree(op);

  		return;
  	}
  
  	init_aggr_kprobe(ap, p);
  	optimize_kprobe(ap);
  }

  #ifdef CONFIG_SYSCTL

  /* This should be called with kprobe_mutex locked */

  static void __kprobes optimize_all_kprobes(void)
  {
  	struct hlist_head *head;
  	struct hlist_node *node;
  	struct kprobe *p;
  	unsigned int i;
  
  	/* If optimization is already allowed, just return */
  	if (kprobes_allow_optimization)
  		return;
  
  	kprobes_allow_optimization = true;

  	for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
  		head = &kprobe_table[i];
  		hlist_for_each_entry_rcu(p, node, head, hlist)
  			if (!kprobe_disabled(p))
  				optimize_kprobe(p);
  	}

  	printk(KERN_INFO "Kprobes globally optimized
  ");
  }

  /* This should be called with kprobe_mutex locked */

  static void __kprobes unoptimize_all_kprobes(void)
  {
  	struct hlist_head *head;
  	struct hlist_node *node;
  	struct kprobe *p;
  	unsigned int i;
  
  	/* If optimization is already prohibited, just return */
  	if (!kprobes_allow_optimization)
  		return;
  
  	kprobes_allow_optimization = false;

  	for (i = 0; i < KPROBE_TABLE_SIZE; i++) {
  		head = &kprobe_table[i];
  		hlist_for_each_entry_rcu(p, node, head, hlist) {
  			if (!kprobe_disabled(p))

  				unoptimize_kprobe(p, false);

  		}
  	}

  	/* Wait for unoptimizing completion */
  	wait_for_kprobe_optimizer();
  	printk(KERN_INFO "Kprobes globally unoptimized
  ");

  }
  
  int sysctl_kprobes_optimization;
  int proc_kprobes_optimization_handler(struct ctl_table *table, int write,
  				      void __user *buffer, size_t *length,
  				      loff_t *ppos)
  {
  	int ret;
  
  	mutex_lock(&kprobe_mutex);
  	sysctl_kprobes_optimization = kprobes_allow_optimization ? 1 : 0;
  	ret = proc_dointvec_minmax(table, write, buffer, length, ppos);
  
  	if (sysctl_kprobes_optimization)
  		optimize_all_kprobes();
  	else
  		unoptimize_all_kprobes();
  	mutex_unlock(&kprobe_mutex);
  
  	return ret;
  }
  #endif /* CONFIG_SYSCTL */

  /* Put a breakpoint for a probe. Must be called with text_mutex locked */

  static void __kprobes __arm_kprobe(struct kprobe *p)
  {

  	struct kprobe *_p;

  
  	/* Check collision with other optimized kprobes */

  	_p = get_optimized_kprobe((unsigned long)p->addr);
  	if (unlikely(_p))

  		/* Fallback to unoptimized kprobe */
  		unoptimize_kprobe(_p, true);

  
  	arch_arm_kprobe(p);
  	optimize_kprobe(p);	/* Try to optimize (add kprobe to a list) */
  }

  /* Remove the breakpoint of a probe. Must be called with text_mutex locked */
  static void __kprobes __disarm_kprobe(struct kprobe *p, bool reopt)

  {

  	struct kprobe *_p;

  	unoptimize_kprobe(p, false);	/* Try to unoptimize */

  	if (!kprobe_queued(p)) {
  		arch_disarm_kprobe(p);
  		/* If another kprobe was blocked, optimize it. */
  		_p = get_optimized_kprobe((unsigned long)p->addr);
  		if (unlikely(_p) && reopt)
  			optimize_kprobe(_p);
  	}
  	/* TODO: reoptimize others after unoptimized this probe */

  }
  
  #else /* !CONFIG_OPTPROBES */
  
  #define optimize_kprobe(p)			do {} while (0)

  #define unoptimize_kprobe(p, f)			do {} while (0)

  #define kill_optimized_kprobe(p)		do {} while (0)
  #define prepare_optimized_kprobe(p)		do {} while (0)
  #define try_to_optimize_kprobe(p)		do {} while (0)
  #define __arm_kprobe(p)				arch_arm_kprobe(p)

  #define __disarm_kprobe(p, o)			arch_disarm_kprobe(p)
  #define kprobe_disarmed(p)			kprobe_disabled(p)
  #define wait_for_kprobe_optimizer()		do {} while (0)

  /* There should be no unused kprobes can be reused without optimization */
  static void reuse_unused_kprobe(struct kprobe *ap)
  {
  	printk(KERN_ERR "Error: There should be no unused kprobe here.
  ");
  	BUG_ON(kprobe_unused(ap));
  }

  static __kprobes void free_aggr_kprobe(struct kprobe *p)
  {

  	arch_remove_kprobe(p);

  	kfree(p);
  }
  
  static __kprobes struct kprobe *alloc_aggr_kprobe(struct kprobe *p)
  {
  	return kzalloc(sizeof(struct kprobe), GFP_KERNEL);
  }
  #endif /* CONFIG_OPTPROBES */

  /* Arm a kprobe with text_mutex */
  static void __kprobes arm_kprobe(struct kprobe *kp)
  {

  	/*
  	 * Here, since __arm_kprobe() doesn't use stop_machine(),
  	 * this doesn't cause deadlock on text_mutex. So, we don't
  	 * need get_online_cpus().
  	 */

  	mutex_lock(&text_mutex);

  	__arm_kprobe(kp);

  	mutex_unlock(&text_mutex);
  }
  
  /* Disarm a kprobe with text_mutex */
  static void __kprobes disarm_kprobe(struct kprobe *kp)
  {

  	/* Ditto */

  	mutex_lock(&text_mutex);

  	__disarm_kprobe(kp, true);

  	mutex_unlock(&text_mutex);
  }

  /*
   * Aggregate handlers for multiple kprobes support - these handlers
   * take care of invoking the individual kprobe handlers on p->list
   */

  static int __kprobes aggr_pre_handler(struct kprobe *p, struct pt_regs *regs)

  {
  	struct kprobe *kp;

  	list_for_each_entry_rcu(kp, &p->list, list) {

  		if (kp->pre_handler && likely(!kprobe_disabled(kp))) {

  			set_kprobe_instance(kp);

  			if (kp->pre_handler(kp, regs))
  				return 1;

  		}

  		reset_kprobe_instance();

  	}
  	return 0;
  }

  static void __kprobes aggr_post_handler(struct kprobe *p, struct pt_regs *regs,
  					unsigned long flags)

  {
  	struct kprobe *kp;

  	list_for_each_entry_rcu(kp, &p->list, list) {

  		if (kp->post_handler && likely(!kprobe_disabled(kp))) {

  			set_kprobe_instance(kp);

  			kp->post_handler(kp, regs, flags);

  			reset_kprobe_instance();

  		}
  	}

  }

  static int __kprobes aggr_fault_handler(struct kprobe *p, struct pt_regs *regs,
  					int trapnr)

  {

  	struct kprobe *cur = __this_cpu_read(kprobe_instance);

  	/*
  	 * if we faulted "during" the execution of a user specified
  	 * probe handler, invoke just that probe's fault handler
  	 */

  	if (cur && cur->fault_handler) {
  		if (cur->fault_handler(cur, regs, trapnr))

  			return 1;
  	}
  	return 0;
  }

  static int __kprobes aggr_break_handler(struct kprobe *p, struct pt_regs *regs)

  {

  	struct kprobe *cur = __this_cpu_read(kprobe_instance);

  	int ret = 0;
  
  	if (cur && cur->break_handler) {
  		if (cur->break_handler(cur, regs))
  			ret = 1;

  	}

  	reset_kprobe_instance();
  	return ret;

  }

  /* Walks the list and increments nmissed count for multiprobe case */
  void __kprobes kprobes_inc_nmissed_count(struct kprobe *p)
  {
  	struct kprobe *kp;

  	if (!kprobe_aggrprobe(p)) {

  		p->nmissed++;
  	} else {
  		list_for_each_entry_rcu(kp, &p->list, list)
  			kp->nmissed++;
  	}
  	return;
  }

  void __kprobes recycle_rp_inst(struct kretprobe_instance *ri,
  				struct hlist_head *head)

  {

  	struct kretprobe *rp = ri->rp;

  	/* remove rp inst off the rprobe_inst_table */
  	hlist_del(&ri->hlist);

  	INIT_HLIST_NODE(&ri->hlist);
  	if (likely(rp)) {
  		spin_lock(&rp->lock);
  		hlist_add_head(&ri->hlist, &rp->free_instances);
  		spin_unlock(&rp->lock);

  	} else
  		/* Unregistering */

  		hlist_add_head(&ri->hlist, head);

  }

  void __kprobes kretprobe_hash_lock(struct task_struct *tsk,

  			 struct hlist_head **head, unsigned long *flags)

  __acquires(hlist_lock)

  {
  	unsigned long hash = hash_ptr(tsk, KPROBE_HASH_BITS);
  	spinlock_t *hlist_lock;
  
  	*head = &kretprobe_inst_table[hash];
  	hlist_lock = kretprobe_table_lock_ptr(hash);
  	spin_lock_irqsave(hlist_lock, *flags);
  }

  static void __kprobes kretprobe_table_lock(unsigned long hash,
  	unsigned long *flags)

  __acquires(hlist_lock)

  {

  	spinlock_t *hlist_lock = kretprobe_table_lock_ptr(hash);
  	spin_lock_irqsave(hlist_lock, *flags);
  }

  void __kprobes kretprobe_hash_unlock(struct task_struct *tsk,
  	unsigned long *flags)

  __releases(hlist_lock)

  {
  	unsigned long hash = hash_ptr(tsk, KPROBE_HASH_BITS);
  	spinlock_t *hlist_lock;
  
  	hlist_lock = kretprobe_table_lock_ptr(hash);
  	spin_unlock_irqrestore(hlist_lock, *flags);
  }

  static void __kprobes kretprobe_table_unlock(unsigned long hash,
         unsigned long *flags)

  __releases(hlist_lock)

  {
  	spinlock_t *hlist_lock = kretprobe_table_lock_ptr(hash);
  	spin_unlock_irqrestore(hlist_lock, *flags);

  }

  /*

   * This function is called from finish_task_switch when task tk becomes dead,
   * so that we can recycle any function-return probe instances associated
   * with this task. These left over instances represent probed functions
   * that have been called but will never return.

   */

  void __kprobes kprobe_flush_task(struct task_struct *tk)

  {

  	struct kretprobe_instance *ri;

  	struct hlist_head *head, empty_rp;

  	struct hlist_node *node, *tmp;

  	unsigned long hash, flags = 0;

  	if (unlikely(!kprobes_initialized))
  		/* Early boot.  kretprobe_table_locks not yet initialized. */
  		return;
  
  	hash = hash_ptr(tk, KPROBE_HASH_BITS);
  	head = &kretprobe_inst_table[hash];
  	kretprobe_table_lock(hash, &flags);

  	hlist_for_each_entry_safe(ri, node, tmp, head, hlist) {
  		if (ri->task == tk)

  			recycle_rp_inst(ri, &empty_rp);

  	}

  	kretprobe_table_unlock(hash, &flags);
  	INIT_HLIST_HEAD(&empty_rp);

  	hlist_for_each_entry_safe(ri, node, tmp, &empty_rp, hlist) {
  		hlist_del(&ri->hlist);
  		kfree(ri);
  	}

  }

  static inline void free_rp_inst(struct kretprobe *rp)
  {
  	struct kretprobe_instance *ri;

  	struct hlist_node *pos, *next;

  	hlist_for_each_entry_safe(ri, pos, next, &rp->free_instances, hlist) {
  		hlist_del(&ri->hlist);

  		kfree(ri);
  	}
  }

  static void __kprobes cleanup_rp_inst(struct kretprobe *rp)
  {

  	unsigned long flags, hash;

  	struct kretprobe_instance *ri;
  	struct hlist_node *pos, *next;

  	struct hlist_head *head;

  	/* No race here */

  	for (hash = 0; hash < KPROBE_TABLE_SIZE; hash++) {
  		kretprobe_table_lock(hash, &flags);
  		head = &kretprobe_inst_table[hash];
  		hlist_for_each_entry_safe(ri, pos, next, head, hlist) {
  			if (ri->rp == rp)
  				ri->rp = NULL;
  		}
  		kretprobe_table_unlock(hash, &flags);

  	}

  	free_rp_inst(rp);
  }

  /*

  * Add the new probe to ap->list. Fail if this is the

  * second jprobe at the address - two jprobes can't coexist
  */

  static int __kprobes add_new_kprobe(struct kprobe *ap, struct kprobe *p)

  {

  	BUG_ON(kprobe_gone(ap) || kprobe_gone(p));

  
  	if (p->break_handler || p->post_handler)

  		unoptimize_kprobe(ap, true);	/* Fall back to normal kprobe */

  	if (p->break_handler) {

  		if (ap->break_handler)

  			return -EEXIST;

  		list_add_tail_rcu(&p->list, &ap->list);
  		ap->break_handler = aggr_break_handler;

  	} else

  		list_add_rcu(&p->list, &ap->list);
  	if (p->post_handler && !ap->post_handler)
  		ap->post_handler = aggr_post_handler;

  
  	if (kprobe_disabled(ap) && !kprobe_disabled(p)) {
  		ap->flags &= ~KPROBE_FLAG_DISABLED;
  		if (!kprobes_all_disarmed)
  			/* Arm the breakpoint again. */

  			__arm_kprobe(ap);

  	}

  	return 0;
  }
  
  /*

   * Fill in the required fields of the "manager kprobe". Replace the
   * earlier kprobe in the hlist with the manager kprobe
   */

  static void __kprobes init_aggr_kprobe(struct kprobe *ap, struct kprobe *p)

  {

  	/* Copy p's insn slot to ap */

  	copy_kprobe(p, ap);

  	flush_insn_slot(ap);

  	ap->addr = p->addr;

  	ap->flags = p->flags & ~KPROBE_FLAG_OPTIMIZED;

  	ap->pre_handler = aggr_pre_handler;

  	ap->fault_handler = aggr_fault_handler;

  	/* We don't care the kprobe which has gone. */
  	if (p->post_handler && !kprobe_gone(p))

  		ap->post_handler = aggr_post_handler;

  	if (p->break_handler && !kprobe_gone(p))

  		ap->break_handler = aggr_break_handler;

  
  	INIT_LIST_HEAD(&ap->list);

  	INIT_HLIST_NODE(&ap->hlist);

  	list_add_rcu(&p->list, &ap->list);

  	hlist_replace_rcu(&p->hlist, &ap->hlist);

  }
  
  /*
   * This is the second or subsequent kprobe at the address - handle
   * the intricacies

   */

  static int __kprobes register_aggr_kprobe(struct kprobe *orig_p,

  					  struct kprobe *p)

  {
  	int ret = 0;

  	struct kprobe *ap = orig_p;

  	if (!kprobe_aggrprobe(orig_p)) {
  		/* If orig_p is not an aggr_kprobe, create new aggr_kprobe. */
  		ap = alloc_aggr_kprobe(orig_p);

  		if (!ap)
  			return -ENOMEM;

  		init_aggr_kprobe(ap, orig_p);

  	} else if (kprobe_unused(ap))

  		/* This probe is going to die. Rescue it */
  		reuse_unused_kprobe(ap);

  
  	if (kprobe_gone(ap)) {

  		/*
  		 * Attempting to insert new probe at the same location that
  		 * had a probe in the module vaddr area which already
  		 * freed. So, the instruction slot has already been
  		 * released. We need a new slot for the new probe.
  		 */

  		ret = arch_prepare_kprobe(ap);

  		if (ret)

  			/*
  			 * Even if fail to allocate new slot, don't need to
  			 * free aggr_probe. It will be used next time, or
  			 * freed by unregister_kprobe.
  			 */

  			return ret;

  		/* Prepare optimized instructions if possible. */
  		prepare_optimized_kprobe(ap);

  		/*

  		 * Clear gone flag to prevent allocating new slot again, and
  		 * set disabled flag because it is not armed yet.

  		 */

  		ap->flags = (ap->flags & ~KPROBE_FLAG_GONE)
  			    | KPROBE_FLAG_DISABLED;

  	}

  	/* Copy ap's insn slot to p */

  	copy_kprobe(ap, p);
  	return add_new_kprobe(ap, p);

  }

  static int __kprobes in_kprobes_functions(unsigned long addr)
  {

  	struct kprobe_blackpoint *kb;

  	if (addr >= (unsigned long)__kprobes_text_start &&
  	    addr < (unsigned long)__kprobes_text_end)

  		return -EINVAL;

  	/*
  	 * If there exists a kprobe_blacklist, verify and
  	 * fail any probe registration in the prohibited area
  	 */
  	for (kb = kprobe_blacklist; kb->name != NULL; kb++) {
  		if (kb->start_addr) {
  			if (addr >= kb->start_addr &&
  			    addr < (kb->start_addr + kb->range))
  				return -EINVAL;
  		}
  	}

  	return 0;
  }

  /*
   * If we have a symbol_name argument, look it up and add the offset field
   * to it. This way, we can specify a relative address to a symbol.
   */
  static kprobe_opcode_t __kprobes *kprobe_addr(struct kprobe *p)
  {
  	kprobe_opcode_t *addr = p->addr;
  	if (p->symbol_name) {
  		if (addr)
  			return NULL;
  		kprobe_lookup_name(p->symbol_name, addr);
  	}
  
  	if (!addr)
  		return NULL;
  	return (kprobe_opcode_t *)(((char *)addr) + p->offset);
  }

  /* Check passed kprobe is valid and return kprobe in kprobe_table. */
  static struct kprobe * __kprobes __get_valid_kprobe(struct kprobe *p)
  {

  	struct kprobe *ap, *list_p;

  	ap = get_kprobe(p->addr);
  	if (unlikely(!ap))

  		return NULL;

  	if (p != ap) {
  		list_for_each_entry_rcu(list_p, &ap->list, list)

  			if (list_p == p)
  			/* kprobe p is a valid probe */
  				goto valid;
  		return NULL;
  	}
  valid:

  	return ap;

  }
  
  /* Return error if the kprobe is being re-registered */
  static inline int check_kprobe_rereg(struct kprobe *p)
  {
  	int ret = 0;

  
  	mutex_lock(&kprobe_mutex);

  	if (__get_valid_kprobe(p))

  		ret = -EINVAL;
  	mutex_unlock(&kprobe_mutex);

  	return ret;
  }

  int __kprobes register_kprobe(struct kprobe *p)

  {
  	int ret = 0;

  	struct kprobe *old_p;

  	struct module *probed_mod;

  	kprobe_opcode_t *addr;

  	addr = kprobe_addr(p);
  	if (!addr)

  		return -EINVAL;

  	p->addr = addr;

  	ret = check_kprobe_rereg(p);
  	if (ret)
  		return ret;

  	jump_label_lock();

  	preempt_disable();

  	if (!kernel_text_address((unsigned long) p->addr) ||

  	    in_kprobes_functions((unsigned long) p->addr) ||

  	    ftrace_text_reserved(p->addr, p->addr) ||

  	    jump_label_text_reserved(p->addr, p->addr))
  		goto fail_with_jump_label;

  	/* User can pass only KPROBE_FLAG_DISABLED to register_kprobe */
  	p->flags &= KPROBE_FLAG_DISABLED;

  	/*
  	 * Check if are we probing a module.
  	 */

  	probed_mod = __module_text_address((unsigned long) p->addr);

  	if (probed_mod) {

  		/*

  		 * We must hold a refcount of the probed module while updating
  		 * its code to prohibit unexpected unloading.

  		 */

  		if (unlikely(!try_module_get(probed_mod)))
  			goto fail_with_jump_label;

  		/*
  		 * If the module freed .init.text, we couldn't insert
  		 * kprobes in there.
  		 */
  		if (within_module_init((unsigned long)p->addr, probed_mod) &&
  		    probed_mod->state != MODULE_STATE_COMING) {
  			module_put(probed_mod);

  			goto fail_with_jump_label;

  		}

  	}

  	preempt_enable();

  	jump_label_unlock();

  	p->nmissed = 0;

  	INIT_LIST_HEAD(&p->list);

  	mutex_lock(&kprobe_mutex);

  	jump_label_lock(); /* needed to call jump_label_text_reserved() */

  	get_online_cpus();	/* For avoiding text_mutex deadlock. */
  	mutex_lock(&text_mutex);

  	old_p = get_kprobe(p->addr);
  	if (old_p) {

  		/* Since this may unoptimize old_p, locking text_mutex. */

  		ret = register_aggr_kprobe(old_p, p);

  		goto out;
  	}

  	ret = arch_prepare_kprobe(p);
  	if (ret)

  		goto out;

  	INIT_HLIST_NODE(&p->hlist);

  	hlist_add_head_rcu(&p->hlist,

  		       &kprobe_table[hash_ptr(p->addr, KPROBE_HASH_BITS)]);

  	if (!kprobes_all_disarmed && !kprobe_disabled(p))

  		__arm_kprobe(p);
  
  	/* Try to optimize kprobe */
  	try_to_optimize_kprobe(p);

  out:

  	mutex_unlock(&text_mutex);
  	put_online_cpus();

  	jump_label_unlock();

  	mutex_unlock(&kprobe_mutex);

  	if (probed_mod)

  		module_put(probed_mod);

  	return ret;

  
  fail_with_jump_label:
  	preempt_enable();
  	jump_label_unlock();
  	return -EINVAL;

  }

  EXPORT_SYMBOL_GPL(register_kprobe);

  /* Check if all probes on the aggrprobe are disabled */
  static int __kprobes aggr_kprobe_disabled(struct kprobe *ap)
  {
  	struct kprobe *kp;
  
  	list_for_each_entry_rcu(kp, &ap->list, list)
  		if (!kprobe_disabled(kp))
  			/*
  			 * There is an active probe on the list.
  			 * We can't disable this ap.
  			 */
  			return 0;
  
  	return 1;
  }
  
  /* Disable one kprobe: Make sure called under kprobe_mutex is locked */
  static struct kprobe *__kprobes __disable_kprobe(struct kprobe *p)
  {
  	struct kprobe *orig_p;
  
  	/* Get an original kprobe for return */
  	orig_p = __get_valid_kprobe(p);
  	if (unlikely(orig_p == NULL))
  		return NULL;
  
  	if (!kprobe_disabled(p)) {
  		/* Disable probe if it is a child probe */
  		if (p != orig_p)
  			p->flags |= KPROBE_FLAG_DISABLED;
  
  		/* Try to disarm and disable this/parent probe */
  		if (p == orig_p || aggr_kprobe_disabled(orig_p)) {
  			disarm_kprobe(orig_p);
  			orig_p->flags |= KPROBE_FLAG_DISABLED;
  		}
  	}
  
  	return orig_p;
  }

  /*
   * Unregister a kprobe without a scheduler synchronization.
   */
  static int __kprobes __unregister_kprobe_top(struct kprobe *p)
  {

  	struct kprobe *ap, *list_p;

  	/* Disable kprobe. This will disarm it if needed. */
  	ap = __disable_kprobe(p);

  	if (ap == NULL)

  		return -EINVAL;

  	if (ap == p)

  		/*

  		 * This probe is an independent(and non-optimized) kprobe
  		 * (not an aggrprobe). Remove from the hash list.

  		 */

  		goto disarmed;
  
  	/* Following process expects this probe is an aggrprobe */
  	WARN_ON(!kprobe_aggrprobe(ap));

  	if (list_is_singular(&ap->list) && kprobe_disarmed(ap))
  		/*
  		 * !disarmed could be happen if the probe is under delayed
  		 * unoptimizing.
  		 */

  		goto disarmed;
  	else {
  		/* If disabling probe has special handlers, update aggrprobe */

  		if (p->break_handler && !kprobe_gone(p))

  			ap->break_handler = NULL;

  		if (p->post_handler && !kprobe_gone(p)) {

  			list_for_each_entry_rcu(list_p, &ap->list, list) {

  				if ((list_p != p) && (list_p->post_handler))
  					goto noclean;
  			}

  			ap->post_handler = NULL;

  		}
  noclean:

  		/*
  		 * Remove from the aggrprobe: this path will do nothing in
  		 * __unregister_kprobe_bottom().
  		 */

  		list_del_rcu(&p->list);

  		if (!kprobe_disabled(ap) && !kprobes_all_disarmed)
  			/*
  			 * Try to optimize this probe again, because post
  			 * handler may have been changed.
  			 */
  			optimize_kprobe(ap);

  	}

  	return 0;

  
  disarmed:

  	BUG_ON(!kprobe_disarmed(ap));

  	hlist_del_rcu(&ap->hlist);
  	return 0;

  }

  static void __kprobes __unregister_kprobe_bottom(struct kprobe *p)
  {

  	struct kprobe *ap;

  	if (list_empty(&p->list))

  		/* This is an independent kprobe */

  		arch_remove_kprobe(p);

  	else if (list_is_singular(&p->list)) {

  		/* This is the last child of an aggrprobe */

  		ap = list_entry(p->list.next, struct kprobe, list);

  		list_del(&p->list);

  		free_aggr_kprobe(ap);

  	}

  	/* Otherwise, do nothing. */

  }

  int __kprobes register_kprobes(struct kprobe **kps, int num)

  {
  	int i, ret = 0;
  
  	if (num <= 0)
  		return -EINVAL;
  	for (i = 0; i < num; i++) {

  		ret = register_kprobe(kps[i]);

  		if (ret < 0) {
  			if (i > 0)
  				unregister_kprobes(kps, i);

  			break;

  		}

  	}

  	return ret;
  }

  EXPORT_SYMBOL_GPL(register_kprobes);

  void __kprobes unregister_kprobe(struct kprobe *p)
  {
  	unregister_kprobes(&p, 1);
  }

  EXPORT_SYMBOL_GPL(unregister_kprobe);

  void __kprobes unregister_kprobes(struct kprobe **kps, int num)
  {
  	int i;
  
  	if (num <= 0)
  		return;
  	mutex_lock(&kprobe_mutex);
  	for (i = 0; i < num; i++)
  		if (__unregister_kprobe_top(kps[i]) < 0)
  			kps[i]->addr = NULL;
  	mutex_unlock(&kprobe_mutex);
  
  	synchronize_sched();
  	for (i = 0; i < num; i++)
  		if (kps[i]->addr)
  			__unregister_kprobe_bottom(kps[i]);

  }

  EXPORT_SYMBOL_GPL(unregister_kprobes);

  
  static struct notifier_block kprobe_exceptions_nb = {
  	.notifier_call = kprobe_exceptions_notify,

  	.priority = 0x7fffffff /* we need to be notified first */
  };

  unsigned long __weak arch_deref_entry_point(void *entry)
  {
  	return (unsigned long)entry;
  }

  int __kprobes register_jprobes(struct jprobe **jps, int num)

  {

  	struct jprobe *jp;
  	int ret = 0, i;

  	if (num <= 0)

  		return -EINVAL;

  	for (i = 0; i < num; i++) {

  		unsigned long addr, offset;

  		jp = jps[i];
  		addr = arch_deref_entry_point(jp->entry);

  		/* Verify probepoint is a function entry point */
  		if (kallsyms_lookup_size_offset(addr, NULL, &offset) &&
  		    offset == 0) {
  			jp->kp.pre_handler = setjmp_pre_handler;
  			jp->kp.break_handler = longjmp_break_handler;
  			ret = register_kprobe(&jp->kp);
  		} else
  			ret = -EINVAL;

  		if (ret < 0) {
  			if (i > 0)
  				unregister_jprobes(jps, i);

  			break;
  		}
  	}
  	return ret;
  }

  EXPORT_SYMBOL_GPL(register_jprobes);

  int __kprobes register_jprobe(struct jprobe *jp)
  {

  	return register_jprobes(&jp, 1);

  }

  EXPORT_SYMBOL_GPL(register_jprobe);

  void __kprobes unregister_jprobe(struct jprobe *jp)

  {

  	unregister_jprobes(&jp, 1);
  }

  EXPORT_SYMBOL_GPL(unregister_jprobe);

  void __kprobes unregister_jprobes(struct jprobe **jps, int num)
  {
  	int i;
  
  	if (num <= 0)
  		return;
  	mutex_lock(&kprobe_mutex);
  	for (i = 0; i < num; i++)
  		if (__unregister_kprobe_top(&jps[i]->kp) < 0)
  			jps[i]->kp.addr = NULL;
  	mutex_unlock(&kprobe_mutex);
  
  	synchronize_sched();
  	for (i = 0; i < num; i++) {
  		if (jps[i]->kp.addr)
  			__unregister_kprobe_bottom(&jps[i]->kp);
  	}

  }

  EXPORT_SYMBOL_GPL(unregister_jprobes);

  #ifdef CONFIG_KRETPROBES

  /*
   * This kprobe pre_handler is registered with every kretprobe. When probe
   * hits it will set up the return probe.
   */
  static int __kprobes pre_handler_kretprobe(struct kprobe *p,
  					   struct pt_regs *regs)
  {
  	struct kretprobe *rp = container_of(p, struct kretprobe, kp);

  	unsigned long hash, flags = 0;
  	struct kretprobe_instance *ri;

  
  	/*TODO: consider to only swap the RA after the last pre_handler fired */

  	hash = hash_ptr(current, KPROBE_HASH_BITS);
  	spin_lock_irqsave(&rp->lock, flags);

  	if (!hlist_empty(&rp->free_instances)) {

  		ri = hlist_entry(rp->free_instances.first,

  				struct kretprobe_instance, hlist);
  		hlist_del(&ri->hlist);
  		spin_unlock_irqrestore(&rp->lock, flags);

  		ri->rp = rp;
  		ri->task = current;

  		if (rp->entry_handler && rp->entry_handler(ri, regs))

  			return 0;

  		arch_prepare_kretprobe(ri, regs);
  
  		/* XXX(hch): why is there no hlist_move_head? */

  		INIT_HLIST_NODE(&ri->hlist);
  		kretprobe_table_lock(hash, &flags);
  		hlist_add_head(&ri->hlist, &kretprobe_inst_table[hash]);
  		kretprobe_table_unlock(hash, &flags);
  	} else {

  		rp->nmissed++;

  		spin_unlock_irqrestore(&rp->lock, flags);
  	}

  	return 0;
  }

  int __kprobes register_kretprobe(struct kretprobe *rp)

  {
  	int ret = 0;
  	struct kretprobe_instance *inst;
  	int i;

  	void *addr;

  
  	if (kretprobe_blacklist_size) {

  		addr = kprobe_addr(&rp->kp);
  		if (!addr)
  			return -EINVAL;

  
  		for (i = 0; kretprobe_blacklist[i].name != NULL; i++) {
  			if (kretprobe_blacklist[i].addr == addr)
  				return -EINVAL;
  		}
  	}

  
  	rp->kp.pre_handler = pre_handler_kretprobe;

  	rp->kp.post_handler = NULL;
  	rp->kp.fault_handler = NULL;
  	rp->kp.break_handler = NULL;

  
  	/* Pre-allocate memory for max kretprobe instances */
  	if (rp->maxactive <= 0) {
  #ifdef CONFIG_PREEMPT

  		rp->maxactive = max_t(unsigned int, 10, 2*num_possible_cpus());

  #else

  		rp->maxactive = num_possible_cpus();

  #endif
  	}

  	spin_lock_init(&rp->lock);

  	INIT_HLIST_HEAD(&rp->free_instances);
  	for (i = 0; i < rp->maxactive; i++) {

  		inst = kmalloc(sizeof(struct kretprobe_instance) +
  			       rp->data_size, GFP_KERNEL);

  		if (inst == NULL) {
  			free_rp_inst(rp);
  			return -ENOMEM;
  		}

  		INIT_HLIST_NODE(&inst->hlist);
  		hlist_add_head(&inst->hlist, &rp->free_instances);

  	}
  
  	rp->nmissed = 0;
  	/* Establish function entry probe point */

  	ret = register_kprobe(&rp->kp);

  	if (ret != 0)

  		free_rp_inst(rp);
  	return ret;
  }

  EXPORT_SYMBOL_GPL(register_kretprobe);

  int __kprobes register_kretprobes(struct kretprobe **rps, int num)

  {
  	int ret = 0, i;
  
  	if (num <= 0)
  		return -EINVAL;
  	for (i = 0; i < num; i++) {

  		ret = register_kretprobe(rps[i]);

  		if (ret < 0) {
  			if (i > 0)
  				unregister_kretprobes(rps, i);

  			break;
  		}
  	}
  	return ret;
  }

  EXPORT_SYMBOL_GPL(register_kretprobes);

  void __kprobes unregister_kretprobe(struct kretprobe *rp)
  {
  	unregister_kretprobes(&rp, 1);
  }

  EXPORT_SYMBOL_GPL(unregister_kretprobe);

  void __kprobes unregister_kretprobes(struct kretprobe **rps, int num)
  {
  	int i;
  
  	if (num <= 0)
  		return;
  	mutex_lock(&kprobe_mutex);
  	for (i = 0; i < num; i++)
  		if (__unregister_kprobe_top(&rps[i]->kp) < 0)
  			rps[i]->kp.addr = NULL;
  	mutex_unlock(&kprobe_mutex);
  
  	synchronize_sched();
  	for (i = 0; i < num; i++) {
  		if (rps[i]->kp.addr) {
  			__unregister_kprobe_bottom(&rps[i]->kp);
  			cleanup_rp_inst(rps[i]);
  		}
  	}
  }

  EXPORT_SYMBOL_GPL(unregister_kretprobes);

  #else /* CONFIG_KRETPROBES */

  int __kprobes register_kretprobe(struct kretprobe *rp)

  {
  	return -ENOSYS;
  }

  EXPORT_SYMBOL_GPL(register_kretprobe);

  int __kprobes register_kretprobes(struct kretprobe **rps, int num)

  {

  	return -ENOSYS;

  }